I have a bright blue betta that cohabits with other smaller tetras in a 20 gallon tank. Yesterday I noticed that he had lighter blue spots on his fins and body- not many but noticable- and they aren't showing up on any of the other fish. I clean the tank often and this is the first time something like this has happened. I was hesitate to treat for ich since it is not white spots. It's almost as if he is faded a bit in those little spots.

By your description and without any other information, that could be any of a huge number of things...
Can you post water params for ammonia, nitrite, nitrate, and pH please?
Temp?
What other fish are in the tank and how many?
What foods are you giving them?
Is there a filter running? If so, what make/model of filter is it?

The more details you can give us the easier it is for us to help. Can you also post a photo of the betta? Of the entire tank? Photos can be very useful when it comes to something like this...